This invention relates to a phthalocyanine composition, a process for preparing the same, an electrophotographic photoreceptor using the same and a coating solution for forming a charge generation layer containing the same.
As a conventional electrophotographic photoreceptor, there may be mentioned a photoreceptor in which about 50 .mu.m of an selenium (Se) film is formed on a conductive substrate such as aluminum by a vacuum vapor deposition method. However, this Se photoreceptor has a problem that it has sensitivity only up to a wavelength of around 500 nm.
Also, there may be mentioned a photoreceptor in which about 50 .mu.m of a Se layer is formed on a conductive substrate, and several .mu.m of a selenium-tellurium (Se--Te) alloy layer is further formed thereon. Whereas this photoreceptor has spectral sensitivity to a longer wavelength as the Te content of the above Se--Te alloy is higher, property of maintaining surface charge becomes worse as the amount of Te added is increased. Thus, there is a serious problem that it cannot be used practically as a photoreceptor.
Also, there may be mentioned the so-called composite two layer type photoreceptor in which a charge generation layer is formed on an aluminum substrate by coating about 1 .mu.m of Chlorocyan Blue or a squaraine derivative, and a charge transport layer is formed thereon by coating 10 to 20 .mu.m of a mixture of polyvinylcarbazole or a pyrazoline derivative and a polycarbonate resin having high insulation resistance. However, this photoreceptor does not have sensitivity to light of 700 nm or more as a matter of fact.
In recent years, there have been reported many composite two layer type photoreceptors in which the above drawbacks have been canceled, that is, those having sensitivity at around 800 nm which is the wavelength of a diode laser oscillation region In many of these, a phthalocyanine pigment is used as a charge generating material, and on a charge generation layer having a film thickness of about 0.5 to 1 .mu.m, a charge transport layer is formed by coating 10 to 20 .mu.m of a mixture having high insulation resistance and comprising a polyvinylcarbazole, a pyrazoline derivative or a hydrazone derivative and a polycarbonate resin or a polyester resin to form a composite two layer type photoreceptor.
In phthalocyanines, not only absorption spectrum and photoconductivity vary depending on central metals, but also these physical properties vary depending on crystal forms. There have been reported several examples of phthalocyanines in which the same central metal is used, but a specific crystal form is selected for an electrophotographic photoreceptor.
For example, there has been reported that various crystal forms exist in titanylphthalocyanines, and charging characteristics, dark decay and sensitivity vary greatly depending on the difference of their crystal forms. In Japanese Provisional Patent Publication No. 49544/1984, it has been described that a crystal form of titanylphthalocyanine giving strong diffraction peaks at 9.2.degree., 13.1.degree., 20.7.degree., 26.2.degree. and 27.1.degree. of Bragg angles (2.theta..+-.0.2.degree.) is preferred, and an X-ray diffraction spectrum chart is shown. Electrophotographic characteristics of a photoreceptor using the titanylphthalocyanine having the crystal form as a charge generating material are dark decay (DDR) of 85% and sensitivity (E.sub.1/2) of 0.57 lux.cndot.sec.
Also, in Japanese Provisional Patent Publication No. 166959/1984, a charge generation layer is obtained by allowing a vapor deposited film of titanylphthalocyanine to stand in tetrahydrofuran-saturated vapor for 1 to 24 hours to change a crystal form.
It has been shown that the X-ray diffraction spectrum shows wide peaks and a smaller number of peaks and gives strong diffraction peaks at 7.5.degree., 12.6.degree., 13.0.degree., 25.4.degree., 26.2.degree. and 28.6.degree. of Bragg angles (2.theta..+-.0.2.degree.).
Electrophotographic characteristics of a photoreceptor using the titanylphthalocyanine having the above crystal form as a charge generating material are dark decay (DDR) of 86% and sensitivity (E.sub.1/2) of 0.7 lux.cndot.sec.
In Japanese Provisional Patent Publication No. 198452/1990, it has been described that a crystal form of titanylphthalocyanine having a main diffraction peak at 27.3.degree. of Bragg angles (2.theta..+-.0.2.degree.) has high sensitivity (1.7 mJ/m.sup.2) and can be prepared by stirring in a mixed solution of water and o-dichlorobenzene under heating at 60.degree. C. for one hour.
In Japanese Provisional Patent Publication No. 256059/1990, it has been described that a crystal form of titanylphthalocyanine having a main diffraction peak at 27.3.degree. of Bragg angles (2.theta..+-.0.2.degree.) has high sensitivity (0.62 lux.cndot.sec) and can be prepared by stirring in 1,2-dichloroethane at room temperature.
In Japanese Provisional Patent Publication No. 194257/1987, it has been described that two or more phthalocyanines are used and, for example, a mixture of titanylphthalocyanine and a non-metal phthalocyanine is used as a charge generating material.
Thus, the phthalocyanines are greatly different in electrophotographic characteristics depending on the difference of crystal forms and the crystal form is an important factor for deciding characteristics of an electrophotographic photoreceptor. Particularly, titanylphthalocyanine provides a charge generating material having extremely high sensitivity and excellent characteristics by changing a crystal form.
However, in a laser beam printer for which it is used, higher quality and higher resolution have been achieved, and an electrophotographic photoreceptor having further high sensitivity characteristic has been demanded.
Therefore, in Japanese Provisional Patent Publication No. 175382/1994, there have been proposed a novel phthalocyanine composition having main diffraction peaks at 7.5.degree., 22.5.degree., 24.3.degree., 25.3.degree. and 28.6.degree. of Bragg angles (2.theta..+-.0.2.degree.) in an X-ray diffraction spectrum with Cu K.alpha., and a process for preparing the same, which comprises precipitating a phthalocyanine mixture containing titanylphthalocyanine and a halogenated metal phthalocyanine in which a central metal is trivalent in water by an acid pasting method and then treating the resulting precipitates with an organic solvent.
This phthalocyanine composition provides a charge generating material having high sensitivity and excellent characteristics by changing a crystal form. However, in a laser printer for which it is used, higher quality and higher resolution have been achieved, and an electrophotographic photoreceptor having further high sensitivity characteristic has been demanded.
In Japanese Provisional Patent Publication No. 271786/1994, there have been proposed a phthalocyanine composition having main diffraction peaks at 7.5.degree., 24.2.degree. and 27.3.degree. of Bragg angles (2.theta..+-.0.2.degree.) in an X-ray diffraction spectrum with Cu K.alpha., and a process for preparing the same. The composition exhibits further high sensitivity characteristic.
According to this process, the above phthalocyanine composition can be prepared simply and easily. However, when the composition is used as a charge generating material of an electrophotographic photoreceptor, there is a problem that electrophotographic characteristics of the electrophotographic photoreceptor are fluctuated delicately depending on the difference in production lot of the phthalocyanine composition. Further, when the electrophotographic photoreceptor is loaded in a laser printer and continuous printing is carried out, there is a problem that electrophotographic characteristics thereof, particularly a dark decay rate, are greatly lowered to worsen printing quality. For this reason, it has been desired to establish a phthalocyanine composition exhibiting excellent characteristics and stability, and preparation conditions under which the phthalocyanine composition can be prepared stably.